The present application is based on and claims priority from Japanese Patent Application 2000-320720 filed Oct. 20, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a planetary gear speed reduction mechanism and, particularly, a bearing of a planetary gear mechanism.
2. Description of the Related Art
A planetary gear speed reduction mechanism used in an engine starter includes a planetary gear supported by a carrier pin via a bearing. The planetary gear is meshed with a sun gear and an internal gear so that the planetary gear can revolve around the sun gear. Accordingly, the bearing has to rotate at a high speed relative to the carrier pin under centrifugal force caused by revolution of the planetary gear. Therefore, it is necessary for the bearing to withstand heavy load and to have good lubricity.
For example, if an oilless bearing is used as the above bearing, a considerable portion of the oil contained in the oilless bearing may fly out under centrifugal force, and the bearing may not be lubricated. In order to hold such oil in the oilless bearing, JP-U-63-164621 proposes an oil-holding felt holder. However, this structure is rather complicated and necessitates additional work time to form an oil holding portion at a bearing case of the planetary gear.
A main object of the invention is to provide a simple and inexpensive bearing structure of the planetary gear speed reduction mechanism.
According to a main feature of the invention, such a bearing is a cylindrical sliding bearing that has a cylindrical inner wall forming an annular grease reservoir around a carrier pin at an end thereof. Preferably, the sliding bearing has grease reservoirs at opposite ends thereof.
The cylindrical inner wall prevents grease from flying away under centrifugal force. Further, the cylindrical inner wall may extend radially inward to hold grease more surely.